Increasing emission standards demands for reduced hazardous exhaust gas emissions and improved fuel economy for automobile engines. Engine performance and its emission generally depend on various parameters, such as, for example, air-fuel ratio, engine pressure, combustion temperature, EGR (Exhaust Gas Recirculation) circulation and ignition timing. Vehicles can include an internal combustion engine that generates drive torque to drive wheels. More specifically, the engine draws in air and mixes the air with fuel to form combustion mixture. The combustion mixture is compressed within cylinders so that the mixture gets combusted in order to drive pistons that are slidably disposed within respective cylinders. The pistons rotatably drive a crankshaft to transfer drive torque to a driveline and ultimately to the wheels. The engine performance can be controlled by measuring various parameters inside the cylinders like pressure, temperature, inside the cylinder, efficiency of combustion and its by-products.
The use of real time cylinder pressure information in advanced diesel engine monitoring and control techniques offer the potential for improved engine reliability and performance as well as reduced levels of emissions. The information on actual pressure developing inside the cylinder can be utilized to control the engine performance, emission control and reduce knocking of the engine. Hence it requires detailed and specified knowledge of the combustion process inside the engine cylinder along with a sophisticated technique in engine diagnostics and control. In recent years, several new sensor technologies have been developed and implemented due to increasing requirements for improved engine performance. A sensor, which is mounted on the engine, needs to possess a very high response time, which requires the measurement of the actual pressure. The engine “knocking” (i.e., auto-ignition and severe pressure pulse is generated in the engine) can be estimated if the transient cylinder pressure is measured. The frequency of knocking signal is a function of cylinder dimension, temperature and which is well know. It is in the order of 5 kHz.
The majority of prior art sensors utilize a piezo-electric element that detects the rate of change of in-cylinder pressure. In general, when the piezo-electric element is used, there are hysteresis characteristics in a relationship between a change in the actual in-cylinder pressure and an output of the in-cylinder pressure sensor. Furthermore, the output of the in-cylinder pressure sensor increases as the temperature of the piezo-electric element increases. When such an in-cylinder pressure sensor is mounted on the engine, variations occur in the output of the in-cylinder pressure sensor due to the heat generation from the engine. They are subject to electromagnetic interference (EMI) effects, have limited lifetime, and are unacceptably expensive.
Similarly lower cost piezoceramic devices, such as spark plug washers and boss-type sensors, do not offer high accuracy under all engine conditions, are subject to electrical interference problems, and are prone to large temperature errors. The degrading effect of alloy segregation, selective oxidation, and diffusion reduces the durability of these sensors and is not sufficient for use in production engines. Similarly, these sensors have limitation in working continuously at very high temperature of about 1000° C.
Another prior art sensor utilizes ionization current signal detection in which a spark plug is used as a sensing probe, to measure the in-cylinder pressure for controlling the performance and emissions of an automobile engine. The ions are generated during combustion and the in cylinder pressure is function of the ion characteristics like magnitude, decay time, etc. The ion current measurement to measure the ionization needs a high voltage source and it is quite complicated and expensive.
FIG. 1 illustrates a prior art graph 10 depicting pressure variation inside engine cylinder versus crank angle. As shown in graph 10 the actual pressure inside the cylinder can be measured and utilized to control the engine performance, emission control and reduce knocking of the engine.
FIG. 2 illustrates a prior art graph 20 depicting pressure variation during engine knocking. The engine cylinder pressure development and its qualified evaluation can be recorded for optimizing activities that are associated with the thermodynamics of power cycle of combustion engine. These results can provide basic information regarding factors such as, for example, engine cylinder pressure development and simulation calculations of theoretical pressure and temperature developments in the cylinder of individual engines can be carried out. The pressure variation during engine knocking, for example, can be measured and utilized to control the knocking via an electronics control unit.
Based on the foregoing it is believed that a need exists for an improved in-cylinder pressure sensor for measuring in-cylinder parameters under very high pressure, high temperature and harsh conditions. It is believed that by utilizing a low cost in-cylinder pressure sensor described in greater detail herein, the engine parameters can potentially be estimated from the measured charge.